Generally, a seat is mounted to a vehicle in such a way as to slide forwards and backwards relative to a vehicle body, thus affording good riding comfort. To this end, a seat rail is provided, thus allowing the seat to slide.
In the case of a car having two rows of seats, a short rail is installed in the car and is used to move the driver's seat and the seat next to the driver's seat. Meanwhile, in the case of an SUV having two or more rows of seats, first and second rows of seats are usually fitted with short rails and the third row of seats and beyond are fitted with long rails to move seats.
In this case, the seat rail is constructed so that an upper track coupled to a seat cushion frame is slidably movable along a lower track mounted to the floor panel in the longitudinal direction of a vehicle body. Further, the seat rail includes a lock unit to restrict the motion of the upper track.
Such a seat rail must be constructed so as to satisfactorily bear the load of a passenger and so that the upper track smoothly slides along the lower track. Preferably, the seat rail is light so as to help reduce fuel consumption.
Further, in order to effectively ensure the safety of passengers, the seat rail must be constructed to provide sufficient strength to bear bending moment of the upper track, which occurs during a head-on collision or a rear-end collision.